Gas discharge lamps as shown in FIG. 9 are known in which the base is formed directly from the glass of the outer bulb of the gas discharge lamp. The base essentially consists of the outside contour of the pinch of the outer bulb of the gas discharge lamp from which the two pins of the gas discharge lamp project, these being used as pins for receptacles of a corresponding lamp holder. For manufacturing related reasons, these pins have a small diameter because of the glass pinch and may have sharp edges at their ends. Due to the manufacturing process, the glass base has a straight edge between the pins. Particularly in the case of low wattage lamps, the spacing between the pins is often so small that a flashover path can form here along the edge of the glass base. Increasing the insulation barrier is difficult to implement for manufacturing related reasons.
However, the gas discharge lamps can also have a ceramic base as shown in FIG. 10. Of course the base does not necessarily have to consist of ceramic, but can be made of many other suitable materials, e.g. special high-temperature plastics such as PPS (polyphenylene sulfide), PEI (polyetherimide) or LCP. Where a ceramic base is referred to in the following explanations, a base is always meant which can consist of a ceramic or another suitable material. In the lamp base, the pins projecting from the lamp bulb are connected to the base contacts which are used in turn as contacts for a corresponding lamp holder. Although said base contacts can be thicker, i.e. implemented with a larger diameter, this reduces the distance between the inner contact surfaces of the base contacts. With these lamps there is likewise the problem of the thin pins which have a very small spacing. Here, however, the flashover path is inside the lamp base which is normally filled with porous ceramic cement in order to establish a connection between the outer bulb of the gas discharge lamp and the base. However, because of the porous structure, this cement is not high voltage resistant, and there is again the problem of possible flashover because of the high field strength.
A combination of the two cases can of course occur here, i.e. a lamp as in FIG. 10 having a lamp base is inserted in a lamp holder. Here there are two regions at risk, namely on the one hand the region in the lamp base in which a flashover path can form along the lower edge of the outer bulb of the gas discharge lamp and, on the other, the region in the bottom of the lamp holder into which the lamp base is inserted. In the following description, the holder bottom and base bottom are regarded as the lower surface of the cavity and inner contour respectively into which the gas discharge lamp 5 is inserted into the holder or the outer bulb is inserted in the lamp base, as the case may be.
As these gas discharge lamps require a high starting voltage, the problem arises that, if the spacing of the pins is too small, an electrical flashover can be produced between the pins which prevents the lamp system from operating properly. An electrical flashover is known to occur where the field strength is so high that the breakdown strength of the insulator or of the air, as the case may be, is exceeded. The highest field strengths are to be found at sharp edges and vertices, basically at all points on electrical conductors whose surfaces have tight bends or more specifically small radii. The critical areas are the regions in which, without a shielding conductor, a high field strength, i.e. a strongly inhomogeneous field, would occur and in which an undesirable flashover can be produced along a clearance or leakage path. Particularly at risk here are the regions which, because of small radii, have very high field strengths which cannot be shielded by suitable insulation. This is particularly the case in the vicinity of the pins. The region will hereinafter be defined as a critical region. Likewise regarded as critical is the region containing the receptacles in the lamp holder. As these likewise cannot be insulated, an electrical flashover may also be produced here. To sum up, it can therefore be said that, in the following explanations, the area around and particularly between the pins and receptacles of the lamp and lamp base respectively or of the lamp holder will be regarded as the critical region.
The market demands increasingly lower-powered gas discharge lamps with smaller lumen packages which are also increasingly smaller physically because of the lower power. However, many of these low wattage lamps do not have a correspondingly smaller starting voltage. The problem therefore arises that the bases of these gas discharge lamps cannot be miniaturized to the extent that would be desirable, without seriously compromising safety/reliability.